A method for preparing a cyclic carbonate

Abstract

The present invention discloses a preparation method of cyclic carbonates, belonging to the technical field of organic catalysis. The present invention provides a catalyst for synthesizing cyclic carbonates. Under a binary organic catalytic system of an ion pair formed by the combination of purine, pyrimidine and an organic strong base, epoxides and carbon dioxide are used to synthesize cyclic carbonates. The catalyst used in this method can be prepared by a one-step method, and the yield can reach more than 90%. The raw materials for synthesizing the catalyst are several purines, pyrimidines and organic strong bases commonly found in organisms, which are commercially available at low cost. At the same time, this type of catalyst does not contain metals or halogens and can synthesize cyclic carbonates under relatively mild conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic catalysis, and particularly relates to a method for synthesizing cyclic carbonates by fixing carbon dioxide with epoxides. Background Art

[0002] Carbon dioxide is one of the main greenhouse gases causing global warming, but at the same time it is also an essential carbon resource indispensable for all life activities. Synthesizing high-value-added chemical products using carbon dioxide as a C1 resource can not only turn waste into treasure but also reduce the emission reduction pressure of carbon dioxide. In recent years, the research on the fixation of carbon dioxide with epoxides to synthesize cyclic carbonates has attracted much attention. Its product cyclic carbonate is widely used in fields such as polyurethane synthesis, green electrolyte batteries, fine chemicals, and pharmaceutical intermediates. Since carbon dioxide molecules themselves have thermal stability and inertness, it is crucial to use effective catalysts to activate carbon dioxide and convert it into useful chemicals for carbon dioxide fixation.

[0003] So far, a series of catalysts have been developed to promote the cycloaddition reaction of carbon dioxide and epoxides, which are mainly divided into two categories: metal catalysts and organic catalysts. Among them, metal catalysts mainly include metal halides, metal oxides, and complexes of transition metals and porphyrins. Organic catalysts mainly include halogen-containing organic catalysts and halogen-free organic catalysts. However, the metal elements remaining in the product carbonate by metal catalysts may limit the application of carbonate in fields such as microelectronics and biomedicine. Moreover, a cocatalyst must be added simultaneously when using metal catalysts to catalyze the cycloaddition reaction, increasing the production cost. The halogen anions in halogen-containing organic catalysts have strong nucleophilicity and are easy to leave, so they are favored, but halogen anions will cause corrosion of the reaction equipment and have an adverse impact on the environment, which limits the industrial application of this type of catalyst. There are few reports on metal-free and halogen-free catalysts, and this patent aims to develop a metal-free and halogen-free catalyst that is cheap and easily available to catalyze the reaction of carbon dioxide and epoxides. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a method for preparing cyclic carbonates from carbon dioxide and epoxides. The catalyst used in this method can be prepared by a one-step method, and the yield can reach more than 90%. The raw materials for synthesizing the catalyst are five purines, pyrimidines, and organic strong bases commonly found in organisms, which are cheap and commercially available. At the same time, this type of catalyst does not contain metals or halogens and can synthesize cyclic carbonates under relatively mild conditions.

[0005] The present invention provides a catalyst for synthesizing cyclic carbonates. An organic strong base reacts with five common purines and pyrimidines in organisms to prepare an ion-pair binary organic catalyst. The ion-pair binary organic catalyst catalyzes the cycloaddition reaction of epoxides and carbon dioxide to obtain cyclic carbonates. The five purines and pyrimidines are selected from the following structures:

[0006]

[0007] The organic strong base is selected from DBU (1,8-diazabicycloundec-7-ene), MTBD (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene), and TBD (1,5,7-triazabicyclo(4.4.0)dec-5-ene); their structures are as follows:

[0008]

[0009] The epoxides are selected from the structures of formula I:

[0010]

[0011] Among them, R 1 , R 2 are selected from H, straight-chain or branched-chain alkyl groups having 1-4 carbon atoms, allyl groups, phenyl groups, halogen or alkyl-substituted phenyl groups, chlorine or bromine-substituted alkyl groups, R 3 -O-CH2-. The R 3 is selected from phenyl groups, phenyl groups substituted with alkyl groups having 1-3 carbon atoms, allyl groups or straight-chain or straight-chain alkyl groups having 1-4 carbon atoms, or R 1 and R 2 are connected to form a six-membered ring or a five-membered ring.

[0012] Preferably, R 1 , R 2 are selected from H, n-butyl, phenyl, halogenated phenyl, R 3 -O-CH2-. The R 3 is selected from phenyl, tolyl, allyl, tert-butyl or methyl.

[0013] Preferably, the ion-pair binary organic catalyst is selected from the following structures:

[0014]

[0015] The epoxides are selected from the following structures:

[0016]

[0017] The structures of the obtained cyclic carbonates are as follows:

[0018]

[0019] The initial pressure of the preparation method is 0.1-2 MPa, the reaction temperature is 25-120° C., the ratio of epoxide to ion-pair binary catalyst is 100:1-100:10, and the ratio of purine or pyrimidine to organic strong base is 1:1-5:1.

[0020] Preferably, the initial pressure of the carbon dioxide is 1 MPa, the reaction temperature is 100 and 120° C., the ratio of epoxide to ion pair binary catalyst is 100:1, and the ratio of purine or pyrimidine to organic strong base is 1 / 1.

[0021] The cyclic carbonate synthesis method

[0022] Add any one of the catalysts 1-15 and any one of the epoxides 16-26 to a reaction vessel, replace the air in the reaction vessel with carbon dioxide three times, fill the reaction vessel with carbon dioxide to 1 MPa, heat to 100 or 120° C. in the absence of a solvent, react for 6 to 24 hours, cool, and obtain the product cyclic carbonate by column chromatography.

[0023] The preparation method of the catalyst comprises the following steps: slowly adding an organic strong base to an aqueous solvent (hot water) of purine and pyrimidine while stirring; reacting the mixture at 25-60° C. for 1-24 hours to obtain a precipitate, which is the target catalyst.

[0024] The organic strong base of the present invention can remove the active NH at position 7 or 3 of purine or pyrimidine, resulting in an ion-pair binary organic catalyst. The purine or pyrimidine anion first combines with carbon dioxide to form a carboxylate anion, which acts as a nucleophile to attack the methylene carbon of the epoxy group. Simultaneously, the organic strong base is protonated, acting as a hydrogen bond donor to coordinate and activate the epoxy group, causing it to ring-open. The oxygen anion formed during the ring-opening acts as a nucleophile to attack the carbonyl carbon, forming a cyclic carbonate compound.

[0025] Beneficial effects:

[0026] (1) The catalyst synthesis method used in the present invention is simple and the raw materials are readily available.

[0027] (2) The present invention provides a method for synthesizing cyclic carbonates from carbon dioxide and epoxides under relatively mild conditions.

[0028] (3) The catalyst used in the present invention does not contain metal, and the resulting product does not contain metal residue, which has great application prospects in the fields of biomedicine and the like; the catalytic system used in the present invention does not contain halogen, is not corrosive to aluminum and iron metal containers, and has great advantages in environmental protection during the production process.

[0029] (4) The reaction process does not require the use of solvents, avoiding the toxicity of organic solvents; the catalyst loading used in the present invention is small, which is beneficial to cost savings.

[0030] (5) The catalytic system used in the present invention consists of two parts (purine, pyrimidine and organic strong base), which has a wide range of tunability and the system is flexible and variable.

[0031] In summary, the present invention has obvious advantages such as simple, mild, efficient, metal-free, halogen-free and solvent-free compared with the existing catalytic systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0033] Figure 1 : 1H NMR spectrum of the catalyst 1 obtained in Example 1

[0034] Figure 2 : 1H NMR spectrum of the catalyst 3 obtained in Example 3

[0035] Figure 3 : 1H NMR spectrum of the catalyst 6 obtained in Example 6

[0036] Figure 4 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 1

[0037] Figure 5 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 13

[0038] Figure 6 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 14

[0039] Figure 7 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 16

[0040] Figure 8 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 18

[0041] Figure 9 : 1H NMR spectrum of the cyclic carbonate product obtained in Example 19 SPECIFIC EMBODIMENTS

[0042] The present invention can be further illustrated by the following examples, and the examples are for illustrative purposes and not for limiting the present invention. Any ordinary technician in the art can understand that these examples do not limit the present invention in any way, and appropriate modifications and data transformations can be made without departing from the essence of the invention and deviating from the scope of the present invention.

[0043] In the examples, the nuclear magnetic resonance hydrogen spectrum was measured using a Bruker Ascend TM-400 nuclear magnetic resonance hydrogen spectrometer from Bruker Corporation. The deuterated reagents used were deuterated chloroform (CDCl3) and deuterated dimethyl sulfoxide (DMSO-d6).

[0044] The structure of the catalytic system used in the examples is as follows:

[0045]

[0046] The structure of the epoxide used in the examples is as follows:

[0047] Structure and number

[0048]

[0049] Example 1

[0050] Preparation of Catalyst 1:

[0051] MTBD (2 mmol, 310 mg) and adenine A (2 mmol, 270 mg) were added to a 50 mL round-bottom flask, and 15 mL of hot water was added as a solvent. The reaction was stirred at 40 °C for 8 hours. After the reaction was completed, the solvent was removed by vacuum method to obtain a crude product. The crude product was placed in a vacuum drying oven for 24 h to dry and remove moisture. 0.57 g of the target catalyst 1 was obtained. Yield (purified) 97.8%. 1 H NMR (400 MHz, DMSO-d6) δ 7.93 (s, 1H), 7.74 (s, 1H), 6.32 (s, 2H), 3.21 (dt, J = 10.9, 5.8 Hz, 8H), 2.88 (s, 3H), 1.90 (p, J = 6.0 Hz, 2H), 1.82 (q, J = 5.9 Hz, 2H). The hydrogen spectrum of the product is as Figure 1 shown.

[0052] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 1 (28.8 mg, 0.1 mmol) and styrene oxide (compound 16, 1.14 mL, 10 mmol) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide 3 times, and then 1 MPa of carbon dioxide gas was charged. It was placed in an oil bath at 120 °C and reacted for 24 hours. After the reaction was completed, it was cooled. After column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product. The nuclear magnetic conversion rate: 93%. 11H NMR (400 MHz, Chloroform-d) δ 7.31–7.21 (m, 5H), 5.53 (t, J = 8.0 Hz, 1H), 4.65 (t, J = 8.4 Hz, 1H), 4.18 (dd, J = 8.7, 7.8 Hz, 1H). The 1H NMR spectrum of the product is as Figure 4 shown.

[0053] Example 2

[0054] Preparation of Catalyst 2:

[0055] MTBD (2 mmol, 310 mg) and guanine G (2 mmol, 300 mg) were added to a 50 mL round-bottom flask, and 15 mL of hot water was added as a solvent. The reaction was stirred at 40 °C for 8 hours. After the reaction was completed, the solvent was removed by vacuum to obtain a crude product. The crude product was placed in a vacuum drying oven for 24 h to dry and remove moisture. 0.59 g of the target catalyst 2 was obtained. Yield (purified) 97%. 1 1H NMR (400 MHz, DMSO-d6) δ 7.48 (s, 1H), 6.42 (s, 2H), 3.20–3.10 (m, 8H), 2.78 (s, 3H), 1.89 (p, J = 6.0 Hz, 2H), 1.76 (p, J = 5.9 Hz, 2H). The 1H NMR spectrum of the product is as Figure 2 shown.

[0056] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 2 (30.4 mg, 0.1 mmol) and styrene oxide (Compound 16, 1.14 mL, 10 mmol) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide 3 times, and then 1 MPa of carbon dioxide gas was charged. It was placed in an oil bath at 120 °C and reacted for 24 hours. After the reaction was completed, it was cooled. After column chromatography separation (petroleum ether:ethyl acetate = 5:1), the product was dried to obtain a pure product. The nuclear magnetic conversion rate: 61%.

[0057] Example 3

[0058] Preparation of Catalyst 3:

[0059] MTBD (2 mmol, 310 mg) and cytosine C (2 mmol, 222 mg) were added to a 50 mL round-bottom flask, and 15 mL of hot water was added as a solvent. The reaction was stirred at 40 °C for 8 hours. After the reaction was completed, the solvent was removed by vacuum to obtain a crude product. The crude product was placed in a vacuum drying oven for 24 h to dry and remove moisture. 0.52 g of the target catalyst 3 was obtained. Yield (purified) 98%. 11H NMR (400 MHz, DMSO-d6) δ 7.31 (d, J = 6.9 Hz, 1H), 6.97 (s, 2H), 5.55 (d, J = 7.0 Hz, 1H), 3.21–2.97 (m, 8H), 2.66 (s, 3H), 1.86 (p, J = 6.0 Hz, 2H), 1.68 (p, J = 5.8 Hz, 2H).

[0060] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 mL). At room temperature, catalyst 3 (26.4 mg, 0.1 mmol) and styrene oxide (Compound 16, 1.14 mL, 10 mmol) were successively added into the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was charged, and it was placed in an oil bath at 120 °C for reaction for 24 hours. After the reaction was completed, it was cooled, and after column chromatography separation (petroleum ether:ethyl acetate = 5:1), the product was dried to obtain a pure product, and the NMR conversion rate was 83%.

[0061] Example 4

[0062] Preparation of catalyst 4:

[0063] MTBD (2 mmol, 310 mg) and thymine T (2 mmol, 252 mg) were added to a 50 mL round-bottom flask, and 15 mL of hot water was added as a solvent, and the reaction was stirred at 40 °C for 8 hours. After the reaction was completed, the solvent was removed by vacuum method to obtain a crude product. The crude product was placed in a vacuum drying oven for 24 h to dry and remove moisture. 0.55 g of the target catalyst 5 was obtained. Yield (purified) 98%. 1 1H NMR (400 MHz, DMSO-d6) δ 7.24 (s, 1H), 3.24–3.13 (m, 8H), 2.82 (s, 3H), 1.90 (p, J = 6.0 Hz, 2H), 1.79 (p, J = 5.9 Hz, 2H), 1.68 (s, 3H).

[0064] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 mL). At room temperature, catalyst 5 (27.9 mg, 0.1 mmol) and styrene oxide (Compound 16, 1.14 mL, 10 mmol) were successively added into the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was charged, and it was placed in an oil bath at 120 °C for reaction for 24 hours. After the reaction was completed, it was cooled, and after column chromatography separation (petroleum ether:ethyl acetate = 5:1), the product was dried to obtain a pure product, and the NMR conversion rate was 86%.

[0065] Example 5

[0066] Preparation of Catalyst 5:

[0067] Add MTBD (2 mmol, 310 mg) and uracil U (2 mmol, 224 mg) into a 50 mL round-bottom flask, add 15 mL of hot water as the solvent, and stir and react at 40 °C for 8 hours. After the reaction, remove the solvent by the vacuum method to obtain the crude product. Put the crude product into a vacuum drying oven and dry it for 24 h to remove moisture. Obtain 0.52 g of the target catalyst 4. Yield (purified): 97%. 1 1H NMR (400 MHz, DMSO-d6) δ 7.40 (d, J = 6.5 Hz, 1H), 5.11 (d, J = 6.5 Hz, 1H), 3.28–3.18 (m, 8H), 2.89 (s, 3H), 1.91 (p, J = 6.0 Hz, 2H), 1.82 (p, J = 6.0 Hz, 2H).

[0068] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, add catalyst 4 (26.5 mg, 0.1 mmol) and styrene oxide (compound 16, 1.14 mL, 10 mmol) into the pressure reaction tube in sequence. Seal the reaction tube, displace the air in the pressure reaction tube with carbon dioxide for 3 times, then charge 1 MPa of carbon dioxide gas, place it in an oil bath at 120 °C, and react for 24 hours. After the reaction, cool it, separate by column chromatography (petroleum ether: ethyl acetate = 5:1), dry the product to obtain the pure product, and the nuclear magnetic conversion rate is 79%.

[0069] Example 6

[0070] Preparation of Catalyst 6:

[0071] Add DBU (2 mmol, 0.3 ml) and adenine A (2 mmol, 270 mg) into a 50 mL round-bottom flask, add 15 mL of hot water as the solvent, and stir and react at 40 °C for 8 hours. After the reaction, remove the solvent by the vacuum method to obtain the crude product. Put the crude product into a vacuum drying oven and dry it for 24 h to remove moisture. Obtain 0.57 g of the target catalyst 6. Yield (purified): 98%. 1 1H NMR (400 MHz, DMSO-d6) δ 7.98 (s, 1H), 7.83 (s, 1H), 6.56 (s, 2H), 3.42–3.31 (m, 4H), 3.21 (t, J = 5.7 Hz, 2H), 2.58–2.52 (m, 2H), 1.81 (p, J = 5.8 Hz, 2H), 1.62–1.51 (m, 6H). The 1H NMR spectrum of the product is as Figure 3 shown.

[0072] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and styrene oxide (Compound 16, 1.14 mL, 10 mmol) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, and then 1 MPa of carbon dioxide gas was charged. The reaction tube was placed in an oil bath at 120 °C and reacted for 24 hours. After the reaction was completed, it was cooled. After column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the NMR conversion rate was 98%.

[0073] Example 7

[0074] Preparation of catalyst 11:

[0075] TBD (2 mmol, 278 mg) and adenine A (2 mmol, 270 mg) were added to a 50 mL round-bottom flask, and 15 mL of hot water was added as a solvent. The mixture was stirred and reacted at 40 °C for 8 hours. After the reaction was completed, the solvent was removed by the vacuum method to obtain a crude product. The crude product was placed in a vacuum drying oven for 24 h to dry and remove moisture. 0.53 g of the target catalyst 11 was obtained. The yield (purification) was 97%. 1 H NMR (400 MHz, DMSO-d6) δ 7.95 (s, 1H), 7.73 (s, 1H), 6.34 (s, 2H), 4.62 (s, 1H), 3.39 (dt, J = 13.4, 5.9 Hz, 8H), 1.91 (tt, J = 7.1, 4.9 Hz, 4H).

[0076] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 11 (27.4 mg, 0.1 mmol) and styrene oxide (Compound 16, 1.14 mL, 10 mmol) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, and then 1 MPa of carbon dioxide gas was charged. The reaction tube was placed in an oil bath at 120 °C and reacted for 24 hours. After the reaction was completed, it was cooled. After column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the NMR conversion rate was 95%.

[0077] Example 8

[0078] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 1 (28.8 mg, 0.1 mmol) and styrene oxide (1.14 mL, 10 mmol, Compound 16) were successively added into the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then charged with 1 MPa of carbon dioxide gas, and placed in an oil bath at 100 °C for 24 hours. After the reaction, it was cooled, and after column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the nuclear magnetic conversion rate was 45%.

[0079] Example 9

[0080] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 1 (72.1 mg, 0.25 mmol) and styrene oxide (1.14 mL, 10 mmol, Compound 16) were successively added into the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then charged with 1 MPa of carbon dioxide gas, and placed in an oil bath at 120 °C for 24 hours. After the reaction, it was cooled, and after column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the nuclear magnetic conversion rate was 91%.

[0081] Example 10

[0082] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 1 (144.2 mg, 0.5 mmol) and styrene oxide (1.14 mL, 10 mmol, Compound 16) were successively added into the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then charged with 1 MPa of carbon dioxide gas, and placed in an oil bath at 120 °C for 24 hours. After the reaction, it was cooled, and after column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the nuclear magnetic conversion rate was 95%.

[0083] Example 11

[0084] Under the Schlenk operation of removing water and oxygen, under the protection of inert gas argon, catalyst 1 (28.8 mg, 0.1 mmol) and styrene oxide (1.14 mL, 10 mmol, Compound 16) were added. The inert gas in the Schlenk tube was replaced with carbon dioxide three times, then a balloon filled with carbon dioxide was tied to the Schlenk tube, and placed in an oil bath at 120 °C for 24 hours. After the reaction, it was cooled, and after column chromatography separation (petroleum ether: ethyl acetate = 5:1), the product was dried to obtain a pure product, and the nuclear magnetic conversion rate was 35%.

[0085] Example 12

[0086] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and (1.2 mL, 10 mmol) butyl ethylene oxide (Compound 17) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was introduced, and it was placed in an oil bath at 120 °C for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was measured by nuclear magnetic resonance quantitative method using 1,3,5-trimethoxybenzene as an internal standard, and a conversion rate of 30% was obtained. 1 H NMR(400MHz,Chloroform-d)δ4.70(qd,J=7.5,5.4Hz,1H),4.52(t,J=8.1Hz,1H),4.06(dd,J=8.4,7.2Hz,1H),1.87–1.71(m,1H),1.74–1.61(m,1H),1.52–1.21(m,4H),0.91(t,J=6.9Hz,3H).

[0087] Example 13

[0088] The cycloaddition reaction of epoxide and CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and (1.42 mL, 10 mmol) tert-butyl glycidyl ether (Compound 18) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was introduced, and it was placed in an oil bath at 120 °C for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was measured by nuclear magnetic resonance quantitative method using 1,3,5-trimethoxybenzene as an internal standard, and a conversion rate of 80% was obtained. 1 H NMR(400MHz,Chloroform-d)δ4.75–4.67(m,1H),4.41(t,J=8.3Hz,1H),4.32(dd,J=8.2,5.8Hz,1H),3.55(dd,J=10.3,4.5Hz,1H),3.46(dd,J=10.3,3.6Hz,1H),1.13(s,9H). The 1H NMR spectrum of the product is as Figure 5 shown.

[0089] Example 14

[0090] The cycloaddition reaction of epoxides with CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol), (28.8 mg, 0.1 mmol), and (0.9 mL, 10 mmol) glycidyl methyl ether (Compound 19) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air inside the pressure reaction tube was replaced with carbon dioxide three times. Then, 1 MPa of carbon dioxide gas was introduced, and the reaction tube was placed in an oil bath at 120 °C for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was measured by nuclear magnetic resonance quantitative method using 1,3,5-trimethoxybenzene as the internal standard, and a conversion rate of 94% was obtained. 1 1H NMR (400 MHz, Chloroform-d) δ 4.76 (ddt, J = 8.3, 6.1, 3.7 Hz, 1H), 4.44 (t, J = 8.4 Hz, 1H), 4.31 (dd, J = 8.4, 6.1 Hz, 1H), 3.59 (dd, J = 11.1, 3.6 Hz, 1H), 3.50 (dd, J = 11.1, 3.8 Hz, 1H), 3.36 (s, 3H). The 1H NMR spectrum of the product is as Figure 6 shown.

[0091] Example 15

[0092] The cycloaddition reaction of epoxides with CO2 was carried out in a pressure reaction tube (internal volume: 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and (1.13 mL, 10 mmol) 1,2-epoxy-5-hexene (Compound 20) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air inside the pressure reaction tube was replaced with carbon dioxide three times. Then, 1 MPa of carbon dioxide gas was introduced, and the reaction tube was placed in an oil bath at 120 °C for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was measured by nuclear magnetic resonance quantitative method using 1,3,5-trimethoxybenzene as the internal standard, and a conversion rate of 18% was obtained. 1 1H NMR (400 MHz, Chloroform-d) δ 5.76 (ddt, J = 16.9, 10.2, 6.6 Hz, 1H), 5.11–4.98 (m, 2H), 4.71 (qd, J = 7.7, 5.1 Hz, 1H), 4.51 (t, J = 8.2 Hz, 1H), 4.06 (dd, J = 8.5, 7.2 Hz, 1H), 2.30–2.08 (m, 2H), 1.90 (dtd, J = 14.0, 8.1, 5.9 HZ, 1H), 1.75 (ddd, J = 14.0, 8.8, 7.0, 5.1 HZ, 1H).

[0093] Example 16

[0094] The cycloaddition reaction of epoxides with CO₂ was carried out in a pressure reaction tube (10 ml internal volume). Catalyst 6 (28.7 mg, 0.1 mmol) and 2-(phenoxymethyl)oxirane (Compound 21) (1.45 mL, 10 mmol) were added sequentially to the pressure reaction tube at room temperature. The reaction tube was sealed, and the air inside was replaced with carbon dioxide three times. Then, 1 MPa of carbon dioxide gas was introduced, and the reaction was allowed to proceed in an oil bath at 120°C for 16 hours. After the reaction was completed, the reaction mixture was cooled, and the epoxide conversion in the reaction solution was determined by nuclear magnetic resonance spectroscopy using 1,3,5-trimethoxybenzene as an internal standard, resulting in a conversion of 99%. 1 HNMR (400 MHz, Chloroform-d) δ 7.26–7.18 (m, 2H), 6.91 (td, J = 7.4, 1.1 Hz, 1H), 6.87–6.81 (m, 2H), 4.05 (ddd, J = 8.0, 5.8, 4.0 Hz, 1H), 3.98 (s, 1H), 3.97 (d, J = 2.7 Hz, 1H), 3.78 (dd, J = 11.5, 3.8 Hz, 1H), 3.68 (dd, J = 11.4, 5.4 Hz, 1H). The hydrogen spectrum of the product is shown in FIG. Figure 7 shown.

[0095] Example 17

[0096] The cycloaddition reaction of epoxides with CO₂ was carried out in a pressure reaction tube (10 ml internal volume). Catalyst 6 (28.7 mg, 0.1 mmol) and allyl glycidyl ether (Compound 22) (1.19 mL, 10 mmol) were added sequentially to the pressure reaction tube at room temperature. The reaction tube was sealed, and the air inside was replaced with carbon dioxide three times. Then, 1 MPa of carbon dioxide gas was introduced, and the reaction was placed in an oil bath at 120°C for 16 hours. After the reaction was completed, the reaction mixture was cooled, and the epoxide conversion in the reaction solution was determined by nuclear magnetic resonance spectroscopy using 1,3,5-trimethoxybenzene as an internal standard, resulting in a conversion of 95%. 1 H NMR(400MHz,Chloroform-d)δ5.86(ddt,J=17.3,10.4,5.6Hz,1H),5.27(dq,J=17.2,1.6HZ,1H),5.21(dq,J=10.4,1.4Hz,1H),4.81(ddt,J=7.9,6 .0,3.8Hz,1H),4.49(t,J=8.4Hz,1H),4.39(dd,J=8.4,6.0Hz,1H),4.11– 3.97(m,2H),3.68(dd,J=11.0,3.9HZ,1H),3.60(dd,J=11.1,3.7HZ,1H).

[0097] Example 18

[0098] The cycloaddition reaction of epoxide with CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and (0.78 mL, 10 mmol) epichlorohydrin (Compound 23) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was charged, and it was placed in an oil bath at 120 °C and reacted for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was determined by NMR quantitative method using 1,3,5-trimethoxybenzene as the internal standard, and a conversion rate of 99% was obtained. 1 H NMR (400 MHz, Chloroform-d) δ 4.94–4.86 (m, 1H), 4.53 (t, J = 8.5 Hz, 1H), 4.35 (dd, J = 8.8, 5.7 Hz, 1H), 3.73–3.65 (m, 2H). The 1H NMR spectrum of the product is as Figure 8 shown.

[0099] Example 19

[0100] The cycloaddition reaction of epoxide with CO2 was carried out in a pressure reaction tube (internal volume 10 ml). At room temperature, catalyst 6 (28.7 mg, 0.1 mmol) and (1.52 mL, 10 mmol) 2-methylphenyl glycidyl ether (Compound 24) were successively added to the pressure reaction tube. The reaction tube was sealed, and the air in the pressure reaction tube was replaced with carbon dioxide three times, then 1 MPa of carbon dioxide gas was charged, and it was placed in an oil bath at 120 °C and reacted for 16 hours. After the reaction was completed, it was cooled, and the conversion rate of the epoxide in the reaction solution was determined by NMR quantitative method using 1,3,5-trimethoxybenzene as the internal standard, and a conversion rate of 96% was obtained. 1 H NMR (400 MHz, Chloroform-d) δ 7.13–7.06 (m, 2H), 6.87 (dd, J = 7.4, 1.1 Hz, 1H), 6.71 (dd, J = 8.5, 1.1 Hz, 1H), 4.98 (ddt, J = 8.6, 5.5, 3.3 Hz, 1H), 4.59–4.48 (m, 2H), 4.19 (dd, J = 10.6, 3.6 Hz, 1H), 4.06 (dd, J = 10.6, 3.1 Hz, 1H). The 1H NMR spectrum of the product is as Figure 9 shown.

Claims

1. A method for preparing a cyclic carbonate, characterized in that: An organic strong base reacts with a purine or pyrimidine represented by Formula I-V to prepare an ion-pair binary organic catalyst, and the ion-pair binary organic catalyst catalyzes the cycloaddition reaction of an epoxide and carbon dioxide to obtain a cyclic carbonate. The organic strong base is selected from DBU, MTBD, and TBD; The structure thereof is as follows: The epoxide is selected from the structure of Formula VI: Among them, R 1 and R 2 are selected from hydrogen, a straight-chain or branched alkyl group having 1 to 4 carbon atoms, an allyl group, a phenyl group, a halogen-substituted phenyl group, R 3 -O-CH2-, and the said R 3 is selected from a phenyl group, a phenyl group substituted by an alkyl group having 1 to 3 carbon atoms, an allyl group or a straight-chain or branched alkyl group having 1 to 4 carbon atoms, or R 1 and R 2 are connected to form a six-membered ring or a five-membered ring.

2. The preparation method according to claim 1, wherein: The epoxide, R 1 , R 2 is selected from H, n-butyl, phenyl, halophenyl, R 3 -O-CH2-, and the R 3 is selected from phenyl, tolyl, allyl, tert-butyl or methyl.

3. The preparation method according to claim 1, characterized in that, The ion-pair binary organic catalyst is selected from the following structures:

4. The preparation method according to claim 1, wherein, The epoxide is selected from the following structures:

5. The preparation method according to claim 1, wherein: The initial pressure of the preparation method of the cyclic carbonate is 0.1-2 MPa, the reaction temperature is 25-120 °C, the molar ratio of the epoxide to the ion-pair binary catalyst is 100:1 to 100:10, and the ratio of the purine or pyrimidine to the organic strong base is 1:1 to 5:

1.

6. The preparation method according to claim 5, characterized in that: The initial pressure of the preparation method of the cyclic carbonate is 1 MPa, the reaction temperatures are 100 °C and 120 °C, the molar ratio of the epoxide to the ion-pair binary catalyst is 100:1, and the molar ratio of the purine or pyrimidine to the organic strong base is 1:1 to 5:

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The preparation method of the catalyst: The aqueous solution of the purine or pyrimidine is slowly added to the organic strong base under stirring. After the addition is completed, the reaction is carried out at 25-60 °C for 1-24 h to obtain a precipitate, and the target catalyst is obtained.

8. The preparation method according to claim 1, characterized in that: The preparation method of the cyclic carbonate is to add an ion-pair binary organic catalyst and an epoxide to a reaction vessel, displace the air in the reaction vessel with carbon dioxide, fill carbon dioxide to 1 MPa, heat to 100 or 120 °C under solvent-free conditions, react for 6-24 h, cool, and the reaction solution is passed through column chromatography to obtain the product cyclic carbonate.

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